Grates of that kind serve for cooling or for other treatment of loose or bulk materials which are piled on to the grate and to which cooling air or another gas is fed from below through the grate surface which is provided with blowing openings.
The grate plates which are arranged in laterally side-by-side relationship on a grate carrier form a row of grates; the whole step grate includes a plurality of rows of grates which are arranged one behind the other in the longitudinal direction, with the grate plates of each row overlapping in scale-like relationship the grate plates of the next following row which adjoins same in a forward direction. In the case of step grates which are in the form of so-called pusher grates individual rows of grates can perform an oscillating movement in the longitudinal direction so that bulk material disposed on the grate is conveyed cyclically forwardly across the grate. Front end walls provided on the grate plates form-the respective rearward boundary of a step. The above-defined directional references such as `laterally side-by-side`, `one behind the other in the longitudinal direction`, `in a forward direction` and the like are used in the same sense in the following description in relation to the grate and the individual grate plates.
A distinction is made between open grate plates and closed grate plates. Open grate plates essentially comprise the cover wall which forms the grate surface and which is provided with blowing openings, and a front end wall which is arranged thereon. In the case of closed grate plates the front end wall is part of a box-like structure which additionally includes a rear wall, side walls and a bottom wall which is provided with an opening for the feed of air.
In the case of non-conveying, fixed step grates the front end walls provided at the grate plates of a step can be supported on the top side of the next following row of grates so that here a harmful gap which affects the grate resistance and the material through-fall rate can be substantially avoided. In contrast, in the case of pusher grates, so-called pusher gaps must be provided between the end wall and the top side of rows of grates which are movable relative to each other in order to prevent wear at that location. The grate resistance and the amount of material which unintentionally drops through the grate inter alia depend on those gaps being calibrated accurately and as closely as possible. It is therefore a matter of great significance for the grate plates to be fixed on the associated grate carrier in such a way that the pusher gaps remain unchanged as far as possible, even under very high mechanical and thermal loadings.
The grate plates can be fixed to the grate carrier by clamping devices which engage on the one hand the grate plate and on the other hand the grate carrier and clamp the grate plate on to the grate carrier. Those clamping devices must in particular be capable of preventing the grate plates from lifting off in order particularly in the case of pusher grates to prevent a harmful increase in the size of the pusher gaps and thus an uncontrolled variation in the grate resistance and the material through-fall rate.
German patent specification No 952 785 describes a step grate which operates as a pusher grate and which uses open grate plates substantially comprising a cover wall and a front end wall. The clamping device includes a tie anchor which, with its end towards the grate plate, engages a hook arranged at the underside of the grate plate while, at its end towards the grate carrier, it passes through an opening formed in a grate carrier wall and is secured by means of screw nuts which can be screwed on to that end. FIGS. 5 and 6 in conjunction with FIG. 1 readily show that assembly of the grate plates is extremely difficult. The tie anchors of each individual grate plate must be fitted into the hook of the grate plate and passed through the opening in the grate carrier wall and then secured by means of a nut and a lock nut, at a location to which access is difficult. The assembly operation is made more difficult in particular by the fact that it has to be carried out from below, that is to say it has to be done `overhead`. Added to that is the fact that, in particular when dealing with repair operations on installations which are already in use, that working area is extremely dirty and, generally just after the installation has been shut down, is also extremely hot, so that, to avoid the assembly personnel suffering from health damage, it is necessary to wait for cooling-down times to elapse and cleaning operations have to be accepted. A further disadvantage is that the hook disposed at the underside of the grate plate is generally not castable so that it must be fixed to the generally cast grate plates, in a separate working operation.
The journal `Zement-Kalk-Gips`, No 4/1992 (45th annual edition), pages 171 ff, in particular FIG. 4, describes a grate plate arrangement for closed grate plates. The grate plates of a row are threaded on to transverse rods or bars, with openings provided in the side walls of the grate plates; the transverse rods or bars are engaged by hook-like tie anchors whose ends towards the grate carriers are passed through an opening in a grate carrier bottom wall and secured by means of a nut which can be screwed on to that end. In relation to this grate plate arrangement also assembly is made difficult by virtue of the fact that the transverse rods or bars to which the tie anchors must be connected are at inaccessible locations into which it is difficult to see so that the assembly operation requires a very great deal of experience. In addition there is also the problem here that the assembly operations have to be carried out overhead and, particularly when dealing with repair operations on installations which are already in use, they have to be performed under hot dirty working conditions. A further disadvantage is that the bending strength of such transverse rods or bars, if of reasonable cross-sectional dimensions, is generally not sufficient to reliably safeguard the grate plates from being lifted off.
The object of the present invention is to provide a secure and reliable grate plate arrangement of the kind having a plurality of side-by-side grates fixed on a grate carrier by a clamping device which permits assembly which is considerably improved and simplified in comparison with the known constructions.